Spark plug



Aug. 19, 1941. P, ANDRES 2,253,220

SPARK PLUG Filed July 1, 1940 Patented Aug. 19, 1941 UNITED STATES \f PATENT OFFICE Seal Fast Corpo corporation of In lana I Application July 1, 1940, Serial No. 343,330 7 2 Claims.

This invention relates to spark plugs commonly employed in gas engines and has for its primary object the provision of a shield about the central electric path thereover but also to serve as a resilient cushion to prevent breakage of the porcelain particularly when the plug is being installed or removed as frequently happens when the spark plug wrench slips and strikes the porcelain.

A further primary object of the invention is to provide a sealing structure cooperating with the insulating shell to aid in forming a shell retaining means and further, to prevent unwarranted disassembling of the plug.

These and other objects and advantages of the invention will become apparent to those versed in the art in the following description of one particular forml of the invention as illustrated in the accompanying drawing, in which Fig. 1 is a side elevation of a plug embodying the invention;

Fig. 2, a top plan view;

Fig. 3, a central vertical section on the line 3-3 in Fig. 2; and

Fig. r4, a transverse section on the line 44 in F18. 3.

Like characters of reference indicate like parts in the several views in the drawing.

A metallic body I is formed in the usual manner to have a central bore therethrough provided with an annular shoulder H on which is seated an insulating gasket |2 preferably 01' a heat conducting type. The usual porcelain I3 is provided with a reduced diameter nose H which extends below the shoulder H in spaced relation from the wall of the bore through the body III to carry insulating porcelain to not only increase the dition, Indianapolis, Ind., it

end so that a spanner wrench or the like may be employed to tighten or loosen the ferrule. By so forming the ferrule, there is no upper projecting part of this member as is the usual case where the seal is completed by a screw-threaded member. This prevents tampering with the plug and requires, that a person equipped with the proper wrench be consulted to disassemble the porcelain from the body. The body I0 is thus to be seen as forming an annular flange 20 extending above the top end of the ferrule |l spaced outwardly from the porcelain l3.

An insulating shell 2| is formed to be generally cylindrical and open at its lower end to telescope over the upper exposed part of the porcelain l3 and have the lower end of the shell 2|flt within the flange 20 and rest by its lower end against the top end of the ferrule H. The upper end of the shell 2| fits over the top end of the porcelain l3 and has a central opening therethrough fitting around the periphery of a washer 22, the washer 22 serving as means for centering the shell 2| about the porcelain. The length of this shell is made to be such that when the securing nut 23 is screwed down on the electrode l5, this nut will serve to retain the shell 2| in position, it not being necessary to provide any great pressure on the shell 2| to retain it. Preferably, although the central electrode l5 and present its lower end centrally of the lower opening into the body Ill. The porcelain l3 has a larger diameter portion above the nose M to extend over and seat on the gasket l2. The porcelain extends upwardly a short distance by this larger diameter and then is reduced in diameter to form a shoulder l6 within the bore of the body In and the porcelain extends on upwardly therebeyond to project from the body In in the usual manner.

A ferrule I1 is screw-threadedly engaged with the wall of the bore in the body Ill and is screwed down against an annular gasket I8 to complete the seal of the porcelain IS in the body Hi. This ferrule when screwed down has its top end spaced slightly below the top end of the body H), as indicated in Fig. 3. In order to turn the ferrule II, it is provided with one or more slots 19, herein shown as two in number, across its upper not necessarily so, but particularly where the upper end of the porcelain I3 is not of a cylindrical shape, as indicated in Fig. 3, the space between the porcelain l3 and the shell 2| is filled with cement 24.

The shell 2| is made out of a resilient material,

any of the synthetic resins being suitable. The

essential characteristics of the materials used are resiliency, high dielectric strength, a sufllcient rigidity to remain in place even when exposed to hot oil, operative temperatures of the engine, and the like. The shell 2| is formed in the nature of a petticoat-type insulator to increase the dielectric path from the upper end portion of the electrode l5 over the shell down to the body III. In the present form, this increased dielectric path is secured by annularly recessing the upper portion of the shell 2| exteriorly thereof to provide a plurality of sharp lips 25, herein shown as four in number, the lower three of which have the shell sloping inwardly therefrom as indicated in Fi 1.

Thus when the plug, assembled as above described, is to be installed, the hexagonal part 26 is engaged with the usual wrench. No other surface of the plug is provided to receive a wrench since the ferrule I1 is entirely concealed and covered over. Should the wrench slip oil. of the part II when the plug is being firmly seated. no damage will be done to the porcelain II should the wrench strike the shell II. The porcelain, as is well known, is quite brittle and fractures readily under sharp impacts, particularly when applied laterally.

While I have herein shown and described my invention in the one particular form, it is obvious that structural changes may be employed without departing from the spirit of the invention and I, therefore, do not desire to be limited to that precise form beyond the limitations as may be imposed by the following claims.

I claim:

1. In combination with a spark plug having a porcelain insulator, an electrode extending therefrom. a metallic body surrounding a length of the porcelain, and means carried by the body to sealably retain the insulator with said body, of a dielectric shell closely surrounding the exposed end of said insulator throughout its length and resting on said retaining means, a cement filling between said shell and said insulator increasing the dielectric gradient therebetween, and, means engaging said electrode and said shell to draw the shell compressibly against said re means, said shell being formed out of material more resilient than said insulator whereby positioning of said shell by said engaging means does not tend to shift said insulator relative to its retaining means.

2. Means for providing a large eifective diameter of the extending end of the insulator in a two piece spark plug of small diameter rating. which consists of the combination of the small diameter body, an insulator having an enlarged intermediate portion for sealing engagement in the body, a metallic ferrule around the insulator above said portion, a separate insulating shell around the insulator above the ferrule, and a cement filling between the insulator and said shell, both the ferrule and the lower end of said shell being fitted to engage within the upper end of said body, said ferrule engaging said body to constitute the second and insulator retaining part of said body, said ferrule being screwthreadedly engaged with the body, and means for turning the ferrule covered by said shell, an electrode extending from the outer end of the insulator, and means engaging the electrode and said shell to center the shell on said insulator means engaging the electrode to retain the shell compressibly against said ferrule, said shell being made of more resilient material than that of the insulator.

PAUL G. ANDRES. 

